The present invention relates to devices for deagglomerating particulate material, that is, reducing the size of particulate material and/or reducing the clumping of particles entrained within a flowing fluid; and more particularly, to a method for deagglomeration and/or attrition of particulate material entrained in a flowing fluid and a deagglomerator for accomplishing the same.
Various methods including electrostatic coating processes utilize particles of a selected size range dispersed in a flowing or quiescent fluid. For example in the electrostatic coating method described in U.S. Pat. No. 4,582,718 entitled "Method And Apparatus For Depositing Nonconductive Material Onto Conductive Filaments" and issued on Apr. 15, 1986 a moving substrate is exposed to a cloud of coating material particles dispersed in a carrier gas and is subjected to the influence of an electrical voltage differential.
In this application, the word "cloud" is used to refer to particulate material dispersed, suspended or entrained in a carrier gas such that the particulate material and the carrier gas move together, although the larger particles may also move under the influence of gravity. Particulate material is solid, not liquid and thus the word "cloud" is used in contrast to the word "aerosol" which is used herein to refer to liquid droplets dispersed, suspended or entrained in a carrier gas. Because of the influence of gravity, the particulate material of a "cloud" is usually less than about 40 microns in diameter.
In order to provide a uniform coating using various electrostatic coating apparatus and procedures, it is necessary to provide particles of a limited and defined range of sizes entrained within air or other carrier gas. This presents a difficulty, since even if the particles are properly sized before they are placed in the carrier gas system of a coating apparatus, spontaneous clumping may occur with the movement of the particles. Furthermore resinous particles are well known to agglomerate. This presents a need for a device for deagglomerating, that is, breaking up clumps and/or otherwise resizing particles, just prior to use.
The term "particle" within this application will be used to refer to discrete fragments of a solid material and also any clumps or other associations of discrete fragments of solid material held together electrostatically or otherwise.
Previous deagglomeration devices have a converging diverging nozzle or a divergent nozzles which separate the flow or energize the particle adjacent the wall to deagglomerate particles. Those deagglomeration devices have shortcomings in that the residence time or turbulence of flow does not allow for sufficient particle accelerations to assure deagglomeration or attrition. Furthermore, some of these prior art devices add significant energy to the particulate flow and may have adverse effects on subsequent processes.
Entraining particulate in gas flow by the use of vortecies for a variety of purposes is also taught in the prior art. Cyclone separators are well known and fluid jet grinders are also well known. However neither are used to produce a cloud of suspended particulate material.
It is therefore highly desirable to provide an improved deagglomerator and an improved method for deagglomerating and/or attrition.
It is also highly desirable to provide an improved deagglomerator and an improved method for deagglomerating which utilize sufficient residence time, rapid particle acceleration, and turbulent flow to assure deagglomeration and/or attrition.
It is also highly desirable to provide an improved deagglomerator and an improved method for deagglomerating having sufficient energy, particle velocities, residence time and turbulent flow to assure deagglomeration and/or attrition of both resinous and non-resinous particles.
It is also highly desirable to provide an improved deagglomerator and an improved method for deagglomerating utilizing minimal additional energy and high particle velocities thereby to assure particle deagglomeration and/or attrition without adverse affects caused by high fluid flow on subsequent processes.
It is finally highly desirable to provide an improved deagglomerator and an improved method for deagglomerating which includes all of the above features.